1. Field of the Invention
The present invention is directed generally to quantum well infrared photodetector focal plane arrays (QWIP FPA""s) and, more particularly, to QWIP FPAs that are capable of detecting multiple colors for determining the temperature of a remote infared source.
2. Background Information
Multicolor infrared detection capability has wide applicability to a number of different applications including aerospace, medical, surveying, mining, and agriculture. For example, multicolor infrared detection can provide useful information during, geographical surveys. Detection in at least two infrared (IR) spectral bands would permit differentiation between man-made structures and natural landscape in a geographical survey. Additionally, in medical applications, multi-color detection would permit improved thermal imaging of the human body for diagnostic purposes.
Multicolor infrared detection has been conventionally performed using a wide-band IR detector and an associated rotating mechanical multicolor filter wheel. The wide-band IR detector detects a broad range of incident wavelengths. The rotating filter wheel selects the desired wavelength that is to be passed to the wide-band detector. An exemplary mechanical color filter wheel system is disclosed in U.S. Pat. No. 5,300,780. Mechanical color wheel systems, however, suffer from a number of deficiencies in multicolor detection. Such systems generally are slow and bulky, require large amounts of power for operation, and have a limited life span. Additionally, color wheel systems tend to have poor photon collection efficiency.
To alleviate some of the known deficiencies of mechanical color filter wheel systems, quantum well photodetectors have been constructed that permit the detection of more than one spectral band. Such detectors are described, for example, in U.S. Pat. Nos. 5,384,469 and 4,903,101. These patents generally disclose the use of a varying bias across a multiple quantum well detector so as to xe2x80x9ctunexe2x80x9d the spectral responsivity of the detector. Thus, in these patents, the xe2x80x9ccolorxe2x80x9d or spectral band that is detected by the quantum well detector is a function of the applied bias voltage. These patents, however, do not disclose the use of multi-color detection for determining the absolute temperature of a remote infrared source. The sensing of the absolute temperature of a remote infrared source can be advantageous in many applications.
Accordingly, there exists a need in the art for a quantum well photo-detector focal plane array that has multi-color capability and which can use the multi-color capability to determine the absolute temperature of remote infrared sources.
Determination of the absolute temperature of remote infrared sources using multi-color detection is achieved in the following exemplary embodiments of the invention. An infrared photo-detector focal plane array includes detectors with quantum well layers that are spectrally xe2x80x9ctunedxe2x80x9d to impinging radiation by modulating the voltage biases applied across each quantum well layer. Read out circuits, interfaced with each detector of the array, process the photo-currents received from each detector to determine the absolute temperature of the remote infrared source from which the impinging radiation originated.
One exemplary embodiment of the present invention is directed to a method of determining a temperature of a remote radiation source comprising the steps of: receiving radiation from said remote source at a detector structure; applying a plurality of bias voltages to said detector structure; obtaining quantities of moving charges in response to said plurality of applied bias voltages; and determining the temperature of said remote radiation source using said quantities of moving charges.
An additional exemplary embodiment of the present invention is directed to a a photo sensitive device comprising: a photodetector for receiving impinging radiation; a voltage source for applying a plurality of bias voltage levels to said photodetector; and a read out circuit for processing moving charges received from said photodetector in response to said impinging radiation and said plurality of bias voltage levels, wherein said read out circuit processes said moving charges in separate circuit paths and wherein each of said separate circuit paths is associated with one of said plurality of bias voltage levels.
A further exemplary embodiment of the present invention is directed to a photo-detector array comprising: a plurality of detector structures for receiving impinging radiation; one or more voltage sources for applying a plurality of voltage levels to each of said plurality of detector structures; and a plurality of read out circuits, wherein each read out circuit processes moving charges, received from an associated detector structure, in separate circuit paths and wherein each of said separate circuit paths is associated with one of said plurality of voltage levels.
An additional exemplary embodiment of the present invention is directed to a method of determining a temperature of a remote radiation source comprising the steps of: receiving radiation from said remote source at a photosensitive device; supplying a first quantity of charges from said photosensitive device to a first charge storage device; supplying a second quantity of charges from said photosensitive device to a second charge storage device; and determining the temperature of said remote radiation source using said first and second quantities of charges.